Method for treating cereal material with a screw transporter

ABSTRACT

There is disclosed a method for treating a cereal with a processing solution by a screw transporter. The screw transporter is preferably a screw extruder or screw conveyer. Also disclosed is a method for using the treated cereal material as a fermentation feedstock. Further, there is disclosed a method for using the treated cereal material in the production of fermentation feedstock.

This application claims priority from U.S. Provisional Application Ser.No. 60/397,982, filed Jul. 23, 2002, the contents of which are hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method for treating a cereal materialwith a processing solution by a screw transporter. The present inventionalso relates to a method for using the treated cereal material as afermentation feedstock and also in the production of a fermentationfeedstock.

BACKGROUND OF THE INVENTION

Grains, including corn, oats, barley, rye, wheat, rice, and sorghumcontain various concentrations of starches, proteins, fiber, and othernutrients. Often, it is desirable to process the grain to isolatevarious fractions or streams that are enriched in one of thesecomponents, for example, to provide a fermentation feedstock. Sincethese components are contained within the grain kernel, most processingmethods begin with a step in which the kernel is treated to expose,separate, concentrate, isolate, or release these raw components, whichmay then be further refined or modified by depolymerization chemicals orenzymes.

To release the raw components of grain kernels, such as corn kernels,typically the corn is processed either by dry milling or wet milling.While dry corn milling requires a smaller operating cost and a smallercapital investment than wet milling, the cost benefits of dry millingmay be offset by poor recovery of corn germ. As such, most cornprocessed in the United States is done by the wet milling process.

The traditional wet milling process includes steeping the corn to softenthe kernels and to aid in separation of the germ, fiber, starch, andprotein. During steeping, the corn absorbs the steeping solution, andthe starch-protein matrix within the corn is disrupted. Typically,steeping is followed by grinding, high speed centrifugation, and/orfiltration to separate corn germ, protein, fiber, and starch. Theindividual components (starch, protein, fiber, germ) then are separatedand purified to provide product streams. These streams may be processedfurther or combined for any purpose such as to provide fermentationfeedstocks.

The wet milling process is an energy and capital intensive process, atleast partially because of the energy requirements to dehydrate excesswater left unabsorbed by the corn during the steeping process.Therefore, a method that minimizes the amount of water necessary totreat the corn during steeping and that facilitates subsequentseparation of various components is desirable.

SUMMARY OF THE INVENTION

This invention relates to a method for treating a cereal materialcomprising treating a cereal material with a processing solution in ascrew transporter and transporting the cereal material through the screwtransporter(s) preferably for at least one hour, and recovering atreated cereal material. The treated cereal material of the presentmethod may be used as is as fermentation feedstock, and may be used inthe production of fermentation feedstock.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a method for treating a cereal materialcomprising treating a cereal material with a processing solution in ascrew transporter and transporting the cereal material through the screwtransporter(s) preferably for at least one hour, and recovering atreated cereal material. The treated cereal material of the presentmethod may be used as is as fermentation feedstock, and may be used inthe production of fermentation feedstock.

The term cereal material is defined as any cereal material or partthereof. Any cereal material, or part thereof, may be treated by thepresent method. The cereal material treated in the present method mayinclude corn, oats, barley, rye, wheat, rice, and sorghum, or a mixturethereof. The cereal material may include whole kernels, or kernels thathave been comminuted. In the case where a comminuted cereal material isused, it may be advantageous to size separate the comminuted cerealmaterial to separate and remove material passing a 10 mesh screen priorto introducing the comminuted cereal material into the screwtransporter.

If it is desired to pre-treat the cereal material a solvent may be used.As solvent there may be used any aqueous or organic solvent or mixturethereof. Examples of organic solvents include hexane, isohexane,ethanol, methanol, propanol, isopropanol, butanol, acetone,dimethylformamide, dimethyl sulfoxide, and the like. Preferred for useis an aqueous solvent such as water containing sulfites, preferablyintroduced as sulfur dioxide and/or salts of bisulfites.

Various additives may be incorporated into the solvents. For example,there may be incorporated additives that enhance the absorption of thesolvent and/ or separation of cereal material into components. Further,there may be incorporated reducing agents and/ or pH adjusting agents;anti-foaming agents; wetting agents and the like. Examples of reducingagents include SO₂ and salts of sulfites and bisulfites,mercartoethanol, thioglycolic acid and the like; suitable pH adjustingagents include lactic acid, acetic acid, hydrochloric acid, sodiumhydroxide, lime and the like. Further more enzymes such as cellulases,hemicellulases, proteases and the like may be utilized.

As used in the present method, a screw transporter is any device thatincludes (1) a screw, such as an auger; and (2) a container, such as abarrel, tube, or trough, wherein cereal material introduced into thescrew transporter is transported as the screw is rotated about its axis.As such, a screw transporter includes screw extruders and screwconveyors. A screw extruder includes a screw located inside a closedchamber, except for input and discharge ports, wherein the containersuch as a barrel or tube encloses the screw. A screw conveyor includes ascrew and an open container such as a trough, wherein the container doesnot completely enclose the screw.

In the present method the cereal material is treated with a processingsolution. The processing solution preferably includes water or othersolvent(s). Any solvent(s) may be utilized such as for example organicsolvents including hexane, isohexane, ethanol, methanol, acetone,propanol, isopropanol, butanol, dimethylformamide, dimethyl sulfoxide,and the like. Preferred for use, is an aqueous solvent such as watercontaining sulphites. The processing solution may optionally includeacid or base to control the pH of the processing solution. Any acid orbase may be utilized such as sodium hydroxide, calcium hydroxide, lacticacid or the like. In addition, the processing solution may optionallycontain other additives such as sulphur dioxide, typically in an amountof about 500-3000 ppm, or an enzyme(s). Suitable enzymes may includeproteases, cellulases, hemicellulases, amylases, or any combinationthereof.

In the present method any amount of processing solution may be used incontacting the cereal material. In a preferred embodiment the processingsolution is added in an amount such that the ratio of processingsolution to cereal material ranges from about 0.30 to about 0.67 m³ ofprocessing solution per metric ton of cereal material (about 2.0 toabout 4.5 gallons of processing solution per bushel of cereal material).In a further preferred embodiment of the method, the processing solutionis introduced in an amount such that the cereal material will completelyabsorb the processing solution.

In the present method the processing solution may be introduced into thescrew transporter(s) at any point. The processing solution may beintroduced into the screw transporter(s) in any manner such as forexample in a co-current or counter current flow in relation to the flowof the cereal material, or added at multiple locations inside the screwtransporter.

The present method for treating cereal material may be carried out atany suitable temperature. In a preferred embodiment the method fortreating the cereal material is carried out at a temperature rangingfrom about 15° C. (59° F.) to about 65° C. (149° F.).

In the present method cereal material is transported by and through thescrew transporter(s). The time in which the cereal material istransported through the screw transporter(s) is preferably at leastabout 1 hour. In a more preferred embodiment the time for transportingthe cereal material ranges from at least about 3 hours to about 10hours.

In the present method there may be used more than one screw transporterfor treating the cereal material. In this instance, between each of theindividual screw transporters, the cereal material may be comminuted.The comminuting of the cereal material is carried out to an extent suchthat 5-90% of the germ is still recoverable as whole germ. In thisembodiment, prior to comminution, water may be added to facilitate thegerm release from the treated cereal material. The germ is recoveredusing any conventional method such as by using hydrocyclones.

The cereal material treated by the present method may be used for anyapplications, particularly where conventionally steeped material hasbeen utilized. In particular the cereal material treated by the presentmethod is expected to be useful as fermentation feedstock. Furthermorethe treated cereal material is expected to be useful in the productionof fermentation feedstock, such as for example for ethanol production.

An exemplary process for carrying out the wet milling of corn treated bythe present method is described as follows:

-   Wet processing of a cereal material may be defined as processing a    cereal material wherein an amount of water exceeding the amount that    can be absorbed by the cereal material is used to enhance separation    of the components of the cereal material. Wet processing may entail    a cereal material or a product resulting from dry grinding the    cereal material. The wet processing and/or the wet milling of a    cereal material will provide a product comprising starch.

The steeped corn product is ground in the presence of mill processwater. Grinding of the steeped corn is performed in three stages. Thefirst stage (herewith referred to as first grind) releases most of thegerm from the steeped corn using a 91 cm (36 inch) grind mill fittedwith Devil's tooth ed plates operating at 900 rpm. The slurry dischargefrom the first grind mill is pressure feed at approximately is 6.2 bars(90 psi) through a two-pass hydrocyclone battery consisting of 15.24 cm(6 inch) hydrocyclones to separate the germ. The separated germ iswashed with mill process water and dried in a rotary drum drier to yielda dried germ product. The remaining slurry from which most germ has beenseparated is milled again, coarsely ground using a second 91 cm (36inch) grind mill (herewith referred as second grind) fitted with Devil'stoothed plates operating at 900 rpm to detach remaining germ from groundcorn in the slurry. Freed germ present in the second grind dischargeslurry is separated and recovered using hydrocyclones as describedabove. After the removal of germ, the remaining corn material is passedover 50 micron screen (referred to as third grind dewatering screen).The filtrate containing starch-protein moves forward, while the cornmaterial retained as overs by the screen is fine ground using a 91 cm(36 inch) grind mill (herewith referred as third grind) fitted withDevil's toothed plates operating at 1800 rpm. The fiber component in theslurry of the third grind discharge is removed by a seven stage screenseparation system arranged such that the fiber is washed in a countercurrent flow of fiber to mill process water, where the cleanest fiber iswashed with the mill process water added to the screen system. Washedfiber is discharged at the last stage (seventh stage), while starch andprotein containing slurry is discharge at the first stage. The screenopening on the first fiber wash stage is 50 micron, followed by 75micron on the second through sixth stage and 150 micron of the laststage. The washed fiber is dewatered using screw presses, and driedusing a rotary drier, resulting in the dried fiber product. Thedischarge from the third grind dewatering screen and first stage fiberwash are combined, creating a slurry with a density of approximately 8Baumé. This slurry is thickened with a Merco H36 centrifuge. Thiscentrifuge operates at 2600 rpm and is fitted with No. 24 size nozzle.The overflow from the centrifuge is used as process water for steeping(also known as mill water), while the underflow slurry, having a Bauméof 12, is fed to a second H36 centrifuge (referred to as primarycentrifuge). The starch-protein in the fed slurry is separated by theprimary centrifuge. The primary centrifuge operates at 2200 rpm and isfitted with No. 24 nozzle to yield an underflow and overflow slurry. Theoverflow slurry is protein-enriched containing approximately 60% (db)protein, while the underflow slurry is starch enriched. The proteinenriched overflow slurry from this centrifugation is then furtherdewatered by centrifugation with a third Merco H36 centrifuge operatingat 2600 rpm, dewatered on a rotary drum filter and dried using a flashdrier. This results in the dried protein rich product, also known ascorn gluten meal. The starch enriched slurry originating from theunderflow of the second Merco H36 centrifuge described above is passedthrough a twelve stage Dorr-Oliver clam shell hydrocyclone starch washbattery. The starch wash battery is designed such that a counter-currentflow between the starch enriched stream entering the first stage of thebattery and potable water entering at the twelfth stage of the batteryis achieved. Each stage starch wash stage has several 10 mm hydroclonesarranged in parallel fashion. Typical feed pressure to each starch washstage, except the twelfth stage, is 6.2 bar (90 psi); the feed pressureon the twelfth stage is 8.27 (120 psi).

-   Purified starch with a slurry density of 23 Baumé is recovered as    underflow from the twelfth stage of the starch wash battery, also    known as starch slurry or starch product of corn wet milling.-   Further information regarding the wet milling of corn is found in    Technology of Corn Wet Milling and Associated Processes p. 69-125,    Paul H. Blanchard, Elsevier Science Publishers B. V. Amsterdam.

The product of wet processing or wet milling comprising starch may beused in any conventional manner. For example, the product of wetprocessing or wet milling comprising starch may be used as afermentation feedstock. In a further embodiment, the product of wetprocessing or wet milling comprising starch product may be processedinto a fermentation feedstock.

As an example of a method for producing a fermentation feedstock, thefollowing is provided. The starch comprising product produced by thepreviously described wet processing or wet milling processes may beoptionally hydrolyzed to form a fermentation feedstock to beincorporated into the fermentation media. The starch slurry may behydrolyzed to any extent to form a hydrolyzed starch, including todextrose. The starch slurry may be hydrolyzed by any manner. Forexample, starch slurry may be hydrolyzed by subjecting the starch slurryto acid hydrolysis. Typically acids will include inorganic acids such ashydrochloric acid and the like. Elevated temperatures increase the rateof hydrolysis and may be varied over a wide range depending on thedegree of hydrolysis desired. Acid hydrolysis is limited in the extentof starch hydrolysis possible. If one wishes to exceed that level ofhydrolysis, one must use other means of hydrolysis such as enzymaticdigestion of the starch with starch hydrolyzing enzymes.

An exemplary process for carrying out starch hydrolysis by acidhydrolysis is described as follows:

-   a) starch slurry with a 23 Baumé is provided;-   b) the pH of the slurry is adjusted to 1.8 with 22 Baumé    hydrochloric acid;-   c) the slurry with pH 1.8 is introduced into a Dedert continuous    acid conversion system (Olympia Fields, Ill., USA) at 146° C. (295°    F.) for 18 minutes, after treatment in the conversion system the    starch is hydrolyzed to 85 dextrose equivalents (DE); and-   d) the pH of the converted starch is then adjusted to 4.8 with 10%    soda ash and cooled.

An exemplary process for starch hydrolysis by enzyme/enzyme hydrolysisis described as follows:

-   Hydrolysis of starch is performed in the following two steps of 1)    liquefaction and 2) saccharification.    -   1) Liquefaction: Water is added to the starch to adjust dry        solid content to 35%. The pH of slurry is adjusted to 5.5 using        sodium hydroxide solution. Calcium chloride is added to the        slurry to have the minimum of 5 ppm of free calcium. TERMAMYL        SUPRA enzyme, (a trademarked amylase available from Novozymes        North America, Inc) is added to this pH adjusted slurry at the        amount of 0.4 liter per metric ton of starch dry solids. Then,        the mixture is heated in a continuous jet cooker to 108° C.        (226.4° F.) and held for 5 minutes in a pressurized vessel. Then        the cooked mixture is cooled to 95° C. (203° F.) and held for        100 minutes. A starch hydrolyzate with a DE of 8 to 12 is        produced.    -   2) Saccharification: Starch hydrolyzate from the above        liquefaction step is cooled to 60° C. and the dry solid content        is adjusted to 32% by adding water. The pH of this diluted        hydrolyzate is adjusted to 4.1-4.3 using sulfuric acid.        DEXTROZYME E enzyme (a trademarked mixture of amyloglucosidase        and pullunase available from Novozymes North America, Inc) is        added at the amount of 0.7 liters per metric ton of dry solids        and then the mixture is held for 40 hours. Dextrose content of        95-97%, on the dry solid basis, is achieved.

Further information regarding starch hydrolysis is found in Technologyof Corn Wet Milling and Associated Processes p. 217-266, Paul H.Blanchard, Elsevier Science Publishers B.V. Amsterdam.

In the present invention any enzyme capable of hydrolyzing a cerealmaterial may be used. Examples of corn hydrolyzing enzymes includestarch hydrolyzing enzymes (for example amylases, pullulanases), proteinhydrolyzing enzymes (for example proteases, peptidases), fiberhydrolyzing enzymes (for example cellulases, xylanases) and phytatehydrolyzing enzymes (for example phytases).

The following examples are presented to illustrate the present inventionand to assist one of ordinary skill in making and using the same. Theexamples are not intended in any way to otherwise limit the scope of theinvention.

EXAMPLES Example 1

A whole grain corn is introduced into an input port or introduction endof a screw transporter. Processing solution is introduced at thedischarge port or position of the screw transporter such that acounter-current flow of processing solution relative to the corn isachieved within the screw extruder. The processing solution compriseswater, 2000 ppm sulphur dioxide and 0.2% (w/w) lactic acid. Theprocessing solution is added at a ratio of about 0.45 m3 of processingsolution per metric ton of the corn (3.0 gallons of processing solutionper bushel of the corn) to achieve a minimum amount of unabsorbedprocessing solution. The time in which the corn is transported in thescrew extruder is about 7 hours, and the temperature of the process ismaintained at about 50° C. The corn and processing solution are passedthrough the transporter continuously. The resulting treated cerealmaterial is recovered. If desired, conventional wet milling separationprocesses may be used for recovering germ, fiber, starch and/or protein.

Example 2

The procedure of example 1 is followed with the following exceptions.Barley is used in place of corn as the cereal material and theprocessing solution is introduced such that a co-current flow relativeto the barley is obtained. There is obtained treated barley. If desiredfiber, starch and/or protein may be separated using conventional wetmilling separation processes.

Example 3

The procedure of example 1 is followed with the following exception. Theprocessing solution comprises sodium hydroxide instead of both sulphurdioxide and lactic acid. The resulting treated cereal material isseparated and recovered.

Example 4

The procedure of example 1 is followed with the following exceptions. Inplace of a single screw transporter there are utilized three screwtransporters in succession. Between each of the three screw transportersthere are employed 91 cm (36 inch) disk mills wherein the corn commutedthe corn.

Example 5

The procedure of example 1 is followed with the following exception. Inplace of the processing solution used in example 1, there is used aprocessing solution comprising of water and 5% w/w thioglycolic acid.

Example 6

The procedure of example 1 is followed with the following exception. Inplace of whole corn, ground corn pieces of size greater than 10 Mesh areused.

The invention has been described with references to various specific andillustrative embodiments and techniques. However, one skilled in artwill recognize that the many variations and modifications may be madewhile remaining within the sprit and scope of the invention.

1. A method for treating a cereal material comprising; treating a cerealmaterial with a processing solution in a screw transporters;transporting the cereal material through the screw transporter(s); andseparating at least one component from the cereal material wherein thecomponents are selected from the group consisting of germ, fiber,protein and starch.
 2. The method according to claim 1 wherein thecereal material is selected from the group consisting of corn, oats,barley, rye, wheat, rice, sorghum and mixtures thereof.
 3. The methodaccording to claim 1, wherein the screw transporter is selected from thegroup consisting of a screw extruder and a screw conveyer.
 4. The methodaccording to claim 1 wherein the cereal material comprises absorbedsolvent selected from the group consisting of an aqueous solvent, anorganic solvent and mixtures thereof.
 5. The method according to claim 4wherein the aqueous solvent is water.
 6. The method according to claim 4wherein the solvent comprises at least one compound selected from thegroup consisting of wetting agents, reducing agents and pH modifiers. 7.The method according to claim 1 wherein the processing solutioncomprises an acid and sulphur dioxide.
 8. The method according to claim7 wherein the acid is lactic acid.
 9. The method according to claim 1wherein the cereal material is treated with processing solution for aperiod of at least 1 hour.
 10. The method according to claim 1 whereinthe cereal material is treated with processing solution for a period ofat least 3 hours.
 11. The method according to claim 1 wherein thetemperature ranges from about 15° C. to about 65° C.
 12. The methodaccording to claim 1 wherein the processing solution is present in anamount ranging from about 0.30 to about 0.67 m³ of processing solutionper metric ton of cereal material (about 2.0 to about 4.5 gallons ofprocessing solution per bushel of cereal material).
 13. The methodaccording to claim 12 wherein the processing solution is present in anamount that will be completely absorbed by the cereal material.
 14. Themethod according to claim 1 wherein more than one screw transporter isutilized.
 15. The method according to claim 14 wherein discharge fromthe screw transporter is comminuted.
 16. (canceled)
 17. The methodaccording to claim 16 wherein the starch containing stream ishydrolyzed.
 18. A method for producing a fermentation feedstockcomprising using the starch containing stream produced in accordancewith claim
 16. 19. A method for producing a fermentation feedstockcomprising using the hydrolyzed starch containing stream produced inaccordance with claim
 17. 20. A method for using the starch containingstream product of claim 16 as fermentation feedstock.
 21. A method forusing the hydrolyzed starch containing stream of claim 17 asfermentation feedstock.